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Old 26-05-2013, 07:48   #61
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Re: battery charging from my generator

Exile,

Your points 2, 3 and 5 are essentially correct.

Here are some real data, not theoretical constructs.

These graphs derive from a specific set of tests carried out by Concorde (Lifeline) in their labs at my request. The objective was to learn more about charge acceptance rates of their AGM batteries, given different size chargers.

Why do this? We were then focused on the COSTS of various strategies to charge batteries on cruising boats and, specifically, our observations that most boats we see with AGM batteries don't have anywhere near enough onboard charging capacity to take advantage of the huge acceptance rate of AGMs.

Concorde was great in carrying out a series of tests for us. These two graphs come out of a test wherein a new 4DL AGM battery was repeatedly discharged to 50% SOC, in ambient 29 degree C conditions, and was charged at 14.4 VDC using (effectively) four different charger sizes: 200% of CA, 50% of CA, 25% of CA, and 10% of CA.

Measurements for each of these four charging conditions were taken every minute for a total of 4 hours, and spreadsheets developed reporting the data and associated calculations.

As is easily seen, at 50% SOC the AGM battery under test initially accepted 127% of its CA in charge current. This dropped rapidly as the charging continued.

Look particularly at where the 200% charger line (blue) crosses the 25% charger line (yellow) at about 35 minutes into the charging. After 35 minutes, the huge charger and the 25% charger were putting the same amount of current into the battery.

Now look at the second graph. I apologize that the color coding isn't uniform. Look at the huge charger line (blue) vs. the 25% charger line (red) at 35 minutes. While both chargers are putting the same amount of current into the battery at this time, the huge charger has already put in about 85% of the AH capacity of the battery, while the 25% charger has only put in about 65%. It will be another 50 minutes or 85 minutes total charge time before the 25% charger reaches this 85% of AH mark, which the huge charger reached in just 35 minutes.

Only a tiny portion of the data provided by Concorde is reflected here. Other data record what happens when higher charging voltages are used, as well as other changes in the charging profile. The data have not been completely analyzed yet. Hopefully, we'll be able to find the time to do that, maybe this winter when we're snowed in :-).

It is instructive to note that most boats we see with AGM batteries have charging capacities (alternators/generators/battery chargers) somewhere in the 10% to 25% range, i.e., woefully too small to take advantage of the AGM battery charge acceptance capacity. And, as Nigel Calder has shown -- using these and other data -- the true costs of charging for these boats is ENORMOUS.

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Old 26-05-2013, 08:00   #62
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Re: battery charging from my generator

OK Dave, I have reread your post a couple of times and see that I was missing the concept of power transfer and how that is viewed a function of the load and not of the source.

It still seems to me a chicken-egg thing in that the regulation of the power supply voltage is through the current that a voltage-choked load can handle. In other words, the supply provides only the current the load can handle. There is no big "tank" of current backed up in the source for the load to "take", and the perspective is that the load has been telling the supply to just provide the right amount of current, so that is what the supply provides.

It seems like the supply is controlling current to me, but I see how it is also seen that the battery can only take that amount of current, so that is what the supply provides. But the supply does not produce or "store up" any extra than that amount. Again, chicken-egg to me.

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Old 26-05-2013, 08:06   #63
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Re: battery charging from my generator

Bill, in those tests, did Concorde comment on battery damage from the higher rates? In other words, is 200% reasonable if it was achievable?

Also, could the true costs be brought down through smaller banks and more usage of existing charging sources (make that 100A charger a 50% CA)? Are people simply installing too large a bank and waiting too long between charges?

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Old 26-05-2013, 09:43   #64
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Originally Posted by colemj View Post
Dave,

In a switch mode supply, how is voltage regulation achieved? My understanding from working with them is that the "on" part of the duty cycle puts energy into a transformer winding. The "off" part transfers that energy (current) into the load (battery in this case).

Voltage regulation is achieved by varying the duty cycle (switching frequency), hence the current stored in the coil (and thusly transferred to the battery).

My whole point is that regulators DO use current control. Given the work by Mr. Ohm, I can't see how they do not.

Yes, I agreed at the start that the battery only accepts the current it can (following Ohm's law). However, that is a strange way of looking at it in my book because the battery is externally forced into a voltage "box" that does not allow it to draw more current.

And that "box" is formed by controlling the current inside the charging source. Even though it is manifested as a voltage to the battery.

Hence, chargers do a lot of current manipulation to keep a battery at a point where it will only accept the current the charger is manipulating. Where am I going wrong with this?

As an aside, I don't think anyone is controlling voltage by zener stacks like Bill suggests (particularly at these currents) - which is why I brought up the zener-FET example that I think is more likely. So how does the zener-FET voltage control work without controlling the current through the collector-emitter? The voltage feedback control is the voltage on the base (gate) of the FET, isn't it? And isn't that from the load (battery)?

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I think this is always much easier to work through with diagrams so written answers always are lacking

Switched mode in essence transfers magnetic energy. Voltage regulation is achieved by sensing the output voltage and comparing it to a reference the resulting error signal controls the duty cycle , lower duty cycles transfer less energy.

Again no power supply ' regulates ' current ? Except in a short circuit. ' its a voltage source therefore current flows as required to maintain the desired output voltage irrespective of load . The regulation is voltage.


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Hence, chargers do a lot of current manipulation to keep a battery at a point where it will only accept the current the charger is manipulating. Where am I going wrong with this?
The charger does not regulate current in normal bulk and absorption mode charging. It regulates voltage and the battery resistance determines current. ( which is why you can use different chargers on a LA battery , the source has no idea of the current characteristics of the load. )

The charger simply regulates voltage and ohms law does the test.

Current regulation is different and isn't normally used on needed in voltage sources. ( only as short circuit or overload protection )

Note the Zener Fet isn't a good example, as FETs are voltage controlled. ( nor is there a collector or emitter ! ) you may be thinking of a Zener and BJT circuit. , BJT s are current controlled devices, but without diagrams lets not try and analyse these simple circuits. The simplest being a series pass regulator where the Zener voltage is maintained at the emitter by the base emitter relationship and as a result output voltage is fixed.

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Old 26-05-2013, 09:54   #65
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Originally Posted by colemj View Post
OK Dave, I have reread your post a couple of times and see that I was missing the concept of power transfer and how that is viewed a function of the load and not of the source.

It still seems to me a chicken-egg thing in that the regulation of the power supply voltage is through the current that a voltage-choked load can handle. In other words, the supply provides only the current the load can handle. There is no big "tank" of current backed up in the source for the load to "take", and the perspective is that the load has been telling the supply to just provide the right amount of current, so that is what the supply provides.

It seems like the supply is controlling current to me, but I see how it is also seen that the battery can only take that amount of current, so that is what the supply provides. But the supply does not produce or "store up" any extra than that amount. Again, chicken-egg to me.

Mark
In a conventional voltage source which a power supply is , you control voltage , current is therefore a function of power demands ( ie the effective load impedance. ) if the load requires more current , its effective input impedance falls , The voltage source transfers as much power as the load needs. But that is not current control ( not in the conventional sense of using the term )

For example in a series pass regulator , in effect you have a voltage controlled resistor. If the load needs less current the effective resistance is raised on the regulator ( the voltage drop over the regulation resistor current being consumed as heat ) , of the load demands more power ( current ) , the series pass resistance is effectively lowered. The net effect is to hold the output voltage steady despite changes in load demands or input voltage change. This is called voltage regulation , or just regulation . Current flows as appropriate accordingly to ohms law, but is not regulated

Again the best possible power supply you can have provides 0 to infinite current while holding its output voltage rock steady , where's the current regulation. ,? , ( ohms law isn't current regulation ) regulation is an active function designed into the circuit


Of course it's a triangular arrangement of resistance , voltage and current. But conventionally we talk of the load current and the source voltage
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Old 26-05-2013, 10:06   #66
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Re: battery charging from my generator

Quote:
Originally Posted by colemj View Post
Bill, in those tests, did Concorde comment on battery damage from the higher rates? In other words, is 200% reasonable if it was achievable?

Also, could the true costs be brought down through smaller banks and more usage of existing charging sources (make that 100A charger a 50% CA)? Are people simply installing too large a bank and waiting too long between charges?

Mark
Good questions, Mark!

Yes, they said the battery will determine how much current it will take at any given SOC (just like I've been saying all along).

They also said that at low SOC, these batteries will initially take 500-600% of their CA and that "this is actually good for the battery".

Of course, few of us with 1000AH house battery banks have 5000-6000 amp charging capacity, so this is really moot :-)

Others with large banks have found that they need to be jogged occasionally with high currents to remain in tip-top condition.

With regard to your second question, there are several options. Yes, I think many boats with AGMs should either have smaller banks or somehow increase their charging capability. Bigger alternators, bigger chargers, multiple chargers, solar panels, wind generators, etc. are all viable options for those who are able to spend the $$$.

Others may find that AGMs are not a good choice. They'd be better off with flooded batteries, especially golf-cart or L-16 size, or with gelled batteries if they need VRLA (sealed) batteries for one reason or another. Both are more tolerant of the 50-85% SOC often prevalent amongst cruisers without either big solar panels or access to shore power.

On a motorboat, of course, there's no problem reaching near-100% SOC, with long engine runs. On a sailboat which is not motoring or motorsailing, this is much harder because -- and I'm going to emphasize this -- it takes a long time to reach 100% SOC, no matter how large the charging source.

This is why solar panels -- with enough capacity to overcome your normal 12VDC draw during the day -- are a good thing to have, because they can provide a constant charging source to the house batteries and help them to reach 100% SOC.

For all types of LA batteries (flooded, AGM, spiral, gels, etc.), one of the biggest killers of capacity is allowing them to stay below full charge for a time and let them sulfate (PbSO4 crystals forming on the plates and, if left there, permanently reducing available plate area for storage of potential energy). So, keep your batteries charged and exercised as well as you can.

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Old 26-05-2013, 10:48   #67
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Exile,

Your points 2, 3 and 5 are essentially correct.

Here are some real data, not theoretical constructs.

These graphs derive from a specific set of tests carried out by Concorde (Lifeline) in their labs at my request. The objective was to learn more about charge acceptance rates of their AGM batteries, given different size chargers.

Why do this? We were then focused on the COSTS of various strategies to charge batteries on cruising boats and, specifically, our observations that most boats we see with AGM batteries don't have anywhere near enough onboard charging capacity to take advantage of the huge acceptance rate of AGMs.

Concorde was great in carrying out a series of tests for us. These two graphs come out of a test wherein a new 4DL AGM battery was repeatedly discharged to 50% SOC, in ambient 29 degree C conditions, and was charged at 14.4 VDC using (effectively) four different charger sizes: 200% of CA, 50% of CA, 25% of CA, and 10% of CA.

Measurements for each of these four charging conditions were taken every minute for a total of 4 hours, and spreadsheets developed reporting the data and associated calculations.

As is easily seen, at 50% SOC the AGM battery under test initially accepted 127% of its CA in charge current. This dropped rapidly as the charging continued.

Look particularly at where the 200% charger line (blue) crosses the 25% charger line (yellow) at about 35 minutes into the charging. After 35 minutes, the huge charger and the 25% charger were putting the same amount of current into the battery.

Now look at the second graph. I apologize that the color coding isn't uniform. Look at the huge charger line (blue) vs. the 25% charger line (red) at 35 minutes. While both chargers are putting the same amount of current into the battery at this time, the huge charger has already put in about 85% of the AH capacity of the battery, while the 25% charger has only put in about 65%. It will be another 50 minutes or 85 minutes total charge time before the 25% charger reaches this 85% of AH mark, which the huge charger reached in just 35 minutes.

Only a tiny portion of the data provided by Concorde is reflected here. Other data record what happens when higher charging voltages are used, as well as other changes in the charging profile. The data have not been completely analyzed yet. Hopefully, we'll be able to find the time to do that, maybe this winter when we're snowed in :-).

It is instructive to note that most boats we see with AGM batteries have charging capacities (alternators/generators/battery chargers) somewhere in the 10% to 25% range, i.e., woefully too small to take advantage of the AGM battery charge acceptance capacity. And, as Nigel Calder has shown -- using these and other data -- the true costs of charging for these boats is ENORMOUS.

Bill
There's nothing unusual in these findings we know that on theory u should charge at or close to the battery's charge acceptance rate for the most efficient charging. In the case of AGMs its rarely the case that you have charging sources close to 100% of the CA of am AGM bank ( its rate even with ordinary LA).

All the more reason why AGMs ate unsuitable for boats. They have characteristics that arnt exploitable and drawbacks that unfortunately are.

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Old 26-05-2013, 22:35   #68
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Re: battery charging from my generator

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This is not correct. The voltage will rise quickly to absorption levels IS because large amounts of current will have been pumped into the battery by the huge charger. ( leaving aside possible damage )

Equally just because the charger ' reaches ' absorption doesn't mean the big charger suddenly stops supplying current , as discussed endlessly , the battery determines the current flow.

So the big charger will bring the batteries ( and the SoC ) out of bulk far quicker then the smaller one and both will take the same time ( approx) in absorption.

Dave
What is not correct? Please elaborate.
Everything I wrote is correct. Every point your are making is the same I am making.

The battery limits the amps it will take for a given voltage. I am not saying that the big charger stops charging at all. I am just saying that the batteries are not accepting the 500 amps at the absorption voltage and the charger will be throttled back into absorption mode by the batteries immediately. Same as you are saying.

So what is wrong?

All I wanted to say is that one can not pick a time after the charger reaches absorption and say at this time the battery is ful or has a certain SOCl. It very much depends on the size of the charger how much time the charger will spend in absorption mode to fill the rest of the capacity.

But, you MAY (I am not sure, never looked into it) be able to pick an amperage in terms of capacity that gives you a fairly reliable indication of the SOC.
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Old 26-05-2013, 22:39   #69
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Re: battery charging from my generator

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Originally Posted by s/v Jedi View Post
Good old LA won't accept much over C/5 anyway.
I assume this means that - no matter the size of the charger, at the absorption voltage of say 14.6V the maximum current going into an LA battery at 50% SOC will be about C/5?
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Old 27-05-2013, 01:27   #70
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Re: battery charging from my generator

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Originally Posted by s/v Jedi View Post
Good old LA won't accept much over C/5 anyway.
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I assume this means that - no matter the size of the charger, at the absorption voltage of say 14.6V the maximum current going into an LA battery at 50% SOC will be about C/5?
At the risk of taking this interesting discussion to another level since I first questioned colemj's post #19 about who controls the charging current, I would like to point readers to Mr Sterling's crazed discussion on "Advanced Battery Charging".

http://www.sterling-power.com/images...edcharging.pdf

He used a 180 amp charger to test a 100AH open flooded LA battery and showed that his chargers would increase the charging by XXX% - to do this the 100Ah battery was accepting 160 amps at 14.8 volts. That is a charge rate of 1.25XC. Even at 14.4 volts it was putting 130 amps into the battery.

So yes an LA battery can accept a much higher charge than C/5, or 20% of the battery capacity - but after 90 mins at 160 amps the battery temperature had risen from 18C to 32C. Mr Sterling maintains that this is well within the battery max voltage of 50C - so this will cause no problems, or excessive gassing!!!!!!!!!!!!!!!!!

He does suggest, elsewhere in his downloads:

“For best effect, use open lead acid batteries, avoid Gel, sealed and AGMs batteries”.

I leave readers to draw their own conclusions on Mr Sterling and his ideas.

btrayfors has already provided excellent graphs and evidence that Lifeline AGMs are designed to accept high charge currents - and they are also Lead Acid Batteries.
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Old 27-05-2013, 02:15   #71
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What is not correct? Please elaborate.
Everything I wrote is correct. Every point your are making is the same I am making.

The battery limits the amps it will take for a given voltage. I am not saying that the big charger stops charging at all. I am just saying that the batteries are not accepting the 500 amps at the absorption voltage and the charger will be throttled back into absorption mode by the batteries immediately. Same as you are saying.

So what is wrong?

All I wanted to say is that one can not pick a time after the charger reaches absorption and say at this time the battery is ful or has a certain SOCl. It very much depends on the size of the charger how much time the charger will spend in absorption mode to fill the rest of the capacity.

But, you MAY (I am not sure, never looked into it) be able to pick an amperage in terms of capacity that gives you a fairly reliable indication of the SOC.
Yes , I agree. , what I disagreed with was your contention that the larger charger suddenly forced the battery in absorption mode and therefore only charged it to 50 %.

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Old 27-05-2013, 02:28   #72
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We need to dispel some myths here.


(A) LA batteries when given a powerful enough charger and a high enough voltage quite happily( or maybe not ) take 1C or more ( AGM , Gels , even more )

(B) with a powerful enough charger and a large enough voltage, LA batteries are like dogs , they will eat themselves sick. You can charge them to destruction.

(5) hence LA is not immune to the size of the charger, its merely immune once the voltage range is controlled. Put on a large power supply and watch that sucker cook !!

This is the general case. However manufacturer regularly recommend lower rates typically C/5 , because (i) safety (ii) heat (iii) the mechanical construction of the plates (iv) gassing and water loss .

What Charles sterling outlines is nothing new , whether its safe and good engineering is another thing altogether.

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Old 27-05-2013, 02:37   #73
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And, yes, for non-believers.....chargers DO in fact control their voltage output in the absorption, float, and equalization stages. How do they do this? Zener diode circuits, or their equivalent, allow chargers to limit their output voltage to any desired level.
You might as an experiment rig up a little Zener controlled series pass regulator , set the regulated voltage to say 10v , then connect that circuit to a 100A LA battery. Come back to me with the output voltage of the regulator ! ( while it lasts )

Chargers only regulate within certain limits , dictated by the size of the competing voltage source and the various intervening impedances.
( a slightly simplified explanation )

Also chargers and PSUs are only current sources, not current sinks , hence they cannot force the battery terminal voltage lower then 0 current in the charger circuit. ( ie terminal voltage 100% determined by the battery , often called float voltage )


Equally chargers can only raise their terminal voltage if the can supply enough current into the load impedance at that point in time. So for examine in bulk mode ( with an average charger ) the charger cannot and is not determining terminal voltage as it cannot supply enough current to do so. Hence it's not regulating voltage at all.


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Old 27-05-2013, 04:19   #74
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Re: battery charging from my generator

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So yes an LA battery can accept a much higher charge than C/5, or 20% of the battery capacity - but after 90 mins at 160 amps the battery temperature had risen from 18C to 32C. Mr Sterling maintains that this is well within the battery max voltage of 50C - so this will cause no problems, or excessive gassing!!!!!!!!!!!!!!!!!
deep cycle led acid batteries....

50 degrees... wouldn't want to go over that , its probably a bit high but not extreme.

Gassing and bubbling is good for mixing the liquid equally throughout the battery.

When using a charger setup for 3 stage marine charging... the battery should not exceed the maximum voltage of 14.8 or 29.6 for 24v.
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Old 27-05-2013, 09:45   #75
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Re: battery charging from my generator

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Yes , I agree. , what I disagreed with was your contention that the larger charger suddenly forced the battery in absorption mode and therefore only charged it to 50 %.

Dave
Thanks. A misunderstanding. That is not what I wanted to say. 50% SOC was just the staring condition for both chargers in this though experiment.
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